1. Field of the Invention
The present invention generally relates to a control for an axial gap type motor/generator having a stator and a rotor arranged to face across from each other along an axial direction. More specifically, the present invention relates to a control configured to prevent or reduce a planar mode of vibration of the rotor in which the rotor deforms in an axial direction.
2. Background Information
The alternating current (AC) motor/generators used as power sources in electric automobiles, hybrid automobiles, and fuel cell automobiles are designed for large outputs. The magnetic noise emitted from this kind of large output AC motor/generator can be a problem. Since the rotational speeds at which such an AC motor/generator is used range widely from a low rotational speed region to a high rotational speed region, rotor vibration occurring when the rotor of the AC motor/generator rotates can also be a problem. There are known technologies for alleviating these problems. One example of such a technology is disclosed in Japanese Laid-Open Patent Publication No. 2005-304237.
The technology disclosed in Japanese Laid-Open Patent Publication No. 2005-304237 increases or decreases a magnetic noise of a multiple phase AC motor/generator by superpositioning different components of a multiple phase alternating current flowing in an armature coil of the motor/generator. More specifically, the different components include a fundamental frequency component and a higher harmonic wave component. The fundamental frequency component is assumed to be a first order frequency component; the higher harmonic wave component has the opposite phase sequence as the fundamental frequency component and is of an order given by n−1 (n is an integer). An nth order magnetic noise is increased or decreased by superpositioning the (n−1)th order higher harmonic wave component over the multiple phase AC current. By using the technology disclosed in Japanese Laid-Open Patent Publication No. 2005-304237, an nth order higher harmonic wave component of a radial magnetic excitation force occurring in the AC motor/generator can be damped. In the technology disclosed in Japanese Laid-Open Patent Publication No. 2005-304237 is applied to a radial gap type motor/generator.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved alternating current control apparatus for an axial gap type motor/generator. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.